Refining raw lacquer

The matured sap is filtered and then stirred, first at room temperature then at 20-45 °C in a specially designed open vessel. The conclusion of the stirring is determined by the changing colour and viscosity of the sap under treatment. The refined urushi produced by this process has a much reduced water content and an appropriate viscosity for coating. During the processing, several important things happen:

  • Excess water is evaporated off, giving 2-4% water content.
  • The polysaccharides in the water droplets are at first precipitated and then broken up into fine particles which become dispersed into the urushiol.
  • There is partial polymerization of some of the urushiol.
  • The urushiol becomes grafted on to glycoproteins and some of these urushiol glycoprotein complexes join up with the finely dispersed polysaccharides (Figure 4.6).

In practice different grades and qualities of lacquer are prepared for use at different stages in the application process.

Wood Working for Amateur Craftsman

Wood Working for Amateur Craftsman

THIS book is one of the series of Handbooks on industrial subjects being published by the Popular Mechanics Company. Like Popular Mechanics Magazine, and like the other books in this series, it is written so you can understand it. The purpose of Popular Mechanics Handbooks is to supply a growing demand for high-class, up-to-date and accurate text-books, suitable for home study as well as for class use, on all mechanical subjects. The textand illustrations, in each instance, have been prepared expressly for this series by well known experts, and revised by the editor of Popular Mechanics.

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